Three-Axis Image Stabilization System

ABSTRACT

An image stabilization system includes an optical assembly configured to receive electromagnetic radiation emitted by a target and produce focused image of the target; a focal plane array, the focal plane array being configured to receive the image and integrate at least a portion of the electromagnetic radiation making up the image to produce an electrical representation of the image; sensors configured to provide kinematic data; a control system receiving the kinematic data and estimating jitter-induced motion of the image on the focal plane and outputting a control signal; and piezo-electric actuators configured to receive the control signal and to translate the focal plane along two orthogonal axes and rotate the focal plane about a third orthogonal axis such that jitter-induced motion of the image on the focal plane is reduced.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation application of U.S.Non-provisional patent application Ser. No. 12/339,444, filed Dec. 19,2008, which claims the benefit under 35 U.S.C. §119(e) of U.S.Provisional Application No. 61/015,631, filed Dec. 20, 2007, both ofwhich are herein incorporated by reference in their entirety.

RIGHTS OF U.S. GOVERNMENT

This disclosure was made with government support under Contract No.NO0173-D-02-2003, awarded by the Naval Research Laboratory. Thegovernment has certain rights in the invention.

BACKGROUND

Dynamic imaging systems, mounted on a moving platform, tracking a movingtarget object, or both, include an aiming structure such as a gimbalassembly and controls to point a camera system independently from theplatform (e.g. aircraft, satellite, vehicle, etc.) on which it ismounted. Meanwhile, the camera system itself may include optics ofvarious types as well as a plane for receiving an image. The plane ofthe image may be a focal plane array (FPA), film, or the like.

One problem of concern to scientists in atmospheric research, as well asthose involved with imaging from aircraft or spacecraft, is theinfluence of jitter in destroying the alignment of a focal plane, suchas that for film or a sensor array. The misalignment may be from anysource, resulting in rotation of the focal plane structures with respectto a mount, optics, or an object being imaged through those optics.Thus, it would be an advance in the art to find a means to stabilize afocal plane array with respect to an image viewed, thus removing asignificant amount of the disparity between the jitter motion of thefocal plane array with respect to the optics, imaged object, etc.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings illustrate various embodiments of theprinciples described herein and are a part of the specification. Theillustrated embodiments are merely examples and do not limit the scopeof the claims.

FIG. 1 is a diagram of an illustrative imaging system, according to oneembodiment of principles described herein.

FIG. 2 is a diagram of rotational axes within an illustrative imagingsystem, according to one embodiment of principles described herein.

FIGS. 3A and 3B are diagrams showing the motion of an image on a focalplane during an integration period, according to one embodiment ofprinciples described herein.

FIG. 4 is a perspective view of an illustrative two axis gimbaledimaging system, according to one embodiment of principles describedherein.

FIG. 5 is a perspective view of an illustrative three axis imagestabilization system, according to one embodiment of principlesdescribed herein.

FIG. 6 is an exploded perspective view of an illustrative three axisimage stabilization system incorporated into a two axis gimbaled imagingsystem, according to one embodiment of principles described herein.

FIG. 7 is a cross-sectional diagram of an illustrative three axis imagestabilization system incorporated into a two axis gimbaled imagingsystem, according to one embodiment of principles described herein.

FIG. 8 is a flow chart showing an illustrative control system for athree axis piezo stabilized imaging system, according to one embodimentof principles described herein.

FIG. 9 is a flow chart of an illustrative method for stabilizing animage system using a three-axis piezoelectric-stabilized, opticalsystem, according to one embodiment of principles described herein.

Throughout the drawings, identical reference numbers designate similar,but not necessarily identical, elements.

DETAILED DESCRIPTION

In view of the foregoing, an apparatus and method in accordance with theinvention provide piezoelectric drivers operating at frequenciesassociated therewith to drive movement of a focal plane array about theeffective center of its optical system.

Electro-optical imaging relies on a focal plane, such as a focal planearray (FPA) of sensors receiving photons (i.e., light, electromagneticradiation), typically integrated over a period of time. The incomingradiation is detected by the sensors to cause a particular intensity ofthe resulting signal. While integrating light, an imaging system orimager (e.g., focal plane array, camera plane, etc.) appears to smear orspread the incoming light over a larger area thereof than shouldaccurately represent the object being imaged in the presence ofvibration in the imaging system.

Smearing degrades image quality. In a sense, smearing represents lostinformation. More accurately, perhaps, smearing represents misplacedinformation that has been distributed over an area larger than it shouldhave been, thus distorting the image and providing misinformation.Nevertheless, the result of smearing ends up typically obscuring thedesirable information of an image.

Vibrating equipment is a simple reality. It is the normal result of thecomplex interactions between pieces of hardware connected in anyconfiguration having a moving part. A system subject to vibration may besubject to numerous modes, frequencies, amplitudes, and othercharacterizations of vibration. Any particular part, item, or system maymove with respect to, or because of an interaction with any otherparticular part connected thereto. This is typically true regardless ofhow securely fastened a part is to another. Vibration isolation may begreater or lesser between different parts in an assembly, and the rangeof transmission may vary widely. The more or less tractable the analysisproblem of determining vibrational modes and frequencies andcompensating for them passively, the more likely will be the need forsome type of active isolation or correction.

Vibration, or relative motion of a focal plane array with respect to itsoptics, or simply with respect to its target is called jitter. Jittermay be characterized as motion at a sufficiently high frequency andamplitude to cause smearing within about an order of magnitude of apicture element (pixel) of a focal plane array. Thus, more than aboutone tenth of a pixel of distance in smearing of an image is oftenunacceptable. A smearing distance of less than about one tenth of apixel is usually satisfactory for many applications of a dynamic camerarelying on a focal plane array.

Various systems exist to control pointing and tracking of cameras andother imaging devices. However, in certain scientific applications, thepointing and stabilization of a platform containing a camera on agimbaled mount is insufficient. For example, the dynamics of aspacecraft, rocket motor, camera, various other equipment, and the like,may introduce vibrations at various frequencies and amplitudes. Acomplete analysis of all possible vibrational frequency sources andresonances consequent thereto is often virtually impossible. Correctionof such vibrations, if known, may not be tractable. Thus, it is notuncommon for a certain amount of “jitter” to exist in some aspect of acamera or other imaging system.

For example, a focal plane array may be thought of as a destination ofrays of electromagnetic radiation (e.g., light) leveraged across afulcrum represented by optical elements, the mounting system, or thelike, while the opposite of the end of that lever represented by the rayis the imaged object, acting as the source or reflector of “light” (e.g.some spectrum of radiation) to be detected by the focal plane array.Accordingly, a comparatively small amount of rotation of a focal planearray in any dimension (e.g., about any axis) represents a comparativelymuch larger displacement of the opposite end of that ray rotated aboutthe fulcrum, at the object or “viewed object” end of the ray.

Consequently, the comparative distance between the focal plane and itsrelated optics, compared to the relative distance between those sameobjects and an object viewed, presents a tremendous multiplier orleverage. Accordingly, in a typical system where, for example, a meterof area in a scanned object or region may be represented by the lighttransmitted to a single pixel of a focal plane array, will be distortedif that focal plane array is allowed to distort or smear by asignificant fraction of the size of a pixel.

In one example, a rotation of a focal plane array resulting in one pixelof displacement of the location of reception of a ray in the focal planearray during an integration period, where that ray represents, forexample, one square meter of a target, can completely smear that squaremeter of target in the resulting image. Accordingly, it is desirable tomaintain stability of a focal plane array within a distance ofapproximately one order of magnitude less than the size of a pixel.

For example, 10 percent of a pixel width variation or jitter may beacceptable, still rendering a substantially clear image. By contrast,jitter on the order of the size of a pixel, which is very likely in anon-stabilized system, will often render an image much less clear ormaybe unusable.

Accordingly, what is needed is a method for very high frequencystabilization of a focal plane array through small displacements. Whatis also needed is a mechanism for stabilizing such a focal plane arrayin accordance with its rate of rotation about three axes, in order tocompensate about those three axes for such rotation due to jitter.

In the following description, for purposes of explanation, numerousspecific details are set forth in order to provide a thoroughunderstanding of the present systems and methods. It will be apparent,however, to one skilled in the art that the present apparatus, systemsand methods may be practiced without these specific details. Referencein the specification to “an embodiment,” “an example” or similarlanguage means that a particular feature, structure, or characteristicdescribed in connection with the embodiment or example is included in atleast that one embodiment, but not necessarily in other embodiments. Thevarious instances of the phrase “in one embodiment” or similar phrasesin various places in the specification are not necessarily all referringto the same embodiment.

FIG. 1 is a diagram of an illustrative imaging system (100) whichincludes a camera body (115) which contains a focal plane (120). A lens(110) contains optics that focus light from an exterior scene (130) ontothe focal plane (120). In this example, the lens (110) accepts lightrays (125) through an aperture (112) and focuses the light rays (125)onto the focal plane (120) to produce an image (135) which is sensed bythe focal plane (120).

The focal plane (120) is made up of a number of pixels (122). Each pixel(122) senses the portion of the image which is focused on it andproduces an electrical signal which is proportional to that portion ofthe image. The number of pixels (122) in the illustrated focal plane(120) has been greatly reduced for clarity of illustration. Modernelectronic camera systems typically include a focal plane made up ofmillions of pixels which provide the imaging resolution required tosense fine details in the exterior scene (130). However, the pixels(122) require a brief “integration time” during which each pixel (122)accumulates electrical charges proportional to the intensity of incidentlight. This “integration time” is analogous to the exposure time in afilm camera. The optimal integration time for an imaging system (100)varies according to a number of factors, including the brightness of theexterior scene (130), the wavelength of light sensed by the focal plane(120), the light gathering capabilities of the lens system (110), andother factors. Ideally, the integration time is long enough for thepixels (122) to convert the incident optical energy into a significantelectrical charge, but not so long that the individual pixels (122)become saturated.

Significant motion of the scene, objects within the scene, or imagingsystem during the integration time results in motion of the image (135)on the focal plane (120). This motion can move light which waspreviously incident on a pixel to neighboring pixels (122). Thisproduces undesirable “smearing” in the image recorded by the focal plane(120). Smearing of the image results in a loss of image quality andinformation. Particularly when fine details in the image are important,such as aerial photography, smearing can unacceptably degrade the imagequality.

Some motions of the imaging system produce less smearing of the opticalimage than others. For example, pure translation of the camera systemwith respect to the scene typically results in low amounts of smearbecause absolute translation of the focal plane array would beinsignificant with respect to an image some kilometers distant. Forexample, one millimeter of displacement in pure translation is simplyone millimeter of displacement with respect to a target.

However, even small rotations of the imaging system can producesignificant amounts of smear. For example one millimeter of motion ofthe focal plane array (120) with respect to an optical fulcrum (128)represents, typically several centimeters, maybe even several meters ofapparent displacement for rays of electromagnetic energy arriving from atargeted object.

FIG. 2 is a diagram which illustrates rotation of an imaging system(100) about three orthogonal axes X, Y, Z. As discussed above, theoptical rays (125, FIG. 1) passing through the lens (110) and strikingthe focal plane (120) can be thought of as a lever with a fulcrum (128)which is relatively close to the focal plane (120). Consequently, asmall motion of the focal plane (120) about the fulcrum (128) canproduce a large shift in the scene (130).

Rotation of the imaging system (100) about the X and Y axes results in atranslation of the image (135, FIG. 1) across the two dimensional focalplane (120). For example, for a scene at a range of 1500 meters, arotation of a given camera about the X or Y axis of a single milliradiancould result in a movement of the field of view by over a meter.Rotation of the imaging system about the Z axis results in acorresponding rotation of the scene on the focal plane. The Z axis, orbore axis, is typically defined as a line which passes through thecenter of the optics and strikes the center of the focal plane (120).The amount of smearing produced from bore axis rotation can be dependenton a number of factors, including the current field of view of thecamera. For example, the edges of a wide angle field of view produced bya fish eye lens would be relativity sensitive to bore axis rotations,while a narrower field of view may be less sensitive.

The human hand typically generates jitter that ranges from 0 to 20 Hz.Consequently, for handheld camera that image within the visiblespectrum, controlling frequencies between 10 Hz and 20 Hz cansignificantly decrease the amount of jitter-induced smear. Forapplications where a camera is attached to a moving vehicle, such as aboat, truck or airplane, higher frequency vibrations can be much moreprevalent. For example, vibration levels from 10 Hz to 500 Hz can besignificant depending on the camera, optics, and focal plane.

FIGS. 3A and 3B illustrate smearing of an image (135) on a focal plane(120) which may result from rotations of the imaging system during anintegration period. FIG. 3A shows the translation of the image (135) onthe focal plane (120) that results from rotations about the X and Yaxes. Specifically, the X translation (305) is produced by rotations ofimaging system (100) about the Y axis and the Y translation (310) isproduced by rotations of imaging system (100) about the X axis. As aresult of these rotations, the image moves across the focal plane duringthe integration period to a second location (300). This produces imagesmear and a corresponding loss of optical quality and information.

FIG. 3B illustrates the effects of rotations of the imaging system aboutthe Z axis, which produces a corresponding rotation of the image (135)on the focal plane. As can be seen from the illustration, thedisplacement of the image (315) on the focal plane is greater on theperimeter of the image than in center of the image. Consequently,imaging systems with larger fields of view can be more sensitive to Zaxis rotation than systems with narrower fields of view.

As discussed above, dynamic imaging systems, such as imaging systems onan aircraft, can produce large amounts of relative motion between theimaging system and the target scene. A gimbaled system can be used topoint the camera at the target scene and to compensate for relativelyslow motions of the aircraft or other platform. FIG. 4 is a perspectiveview of an illustrative two axis gimbaled imaging system (400). Thegimbaled imaging system (400) uses a two axis gimbal (405) to supportand point a ball (410) which contains the lens and focal plane. Typicalgimbaled systems provide an elevation rotation (420) about an X axis andan azimuth rotation (425) about a Y axis. By actuating motors whichcontrol motion about these two axes, the ball (410) can be oriented sothat imaging systems looking out from one or more apertures (415) can bepointed in any direction within the range of motion provided by thegimbal. Consequently, the two axis gimbal can point the imaging systemat a target or move across a scene independently from the motion of themobile platform. The gimbaled imaging system (400) is a relativelymassive device and consequently can typically only compensate for slowermotions (such as motions below about 10 Hz). Further, the gimbaledimaging system (400) has extremely limited ability to compensate forrotations about the bore axis. Undesirable bore axis rotations canfrequently occur in aircraft optical sensors as the result of pitch,roll, and heading perturbations in the aircraft motion.

As discussed above, higher frequency motions of the platform can also beproduced by a mobile platform or the surrounding environment. Forexample, on an aircraft mounted optical system, vibrations produced bymechanical motion and turbulence can produce undesirable jitter andcorresponding smear of the images. The gimbal (405) is unable tocompensate for this higher frequency motion or rotations about the boresight of the optical sensor. Consequently, to reliably produce highquality imagery, an image stabilization system may be incorporatedwithin the optical system.

FIG. 5 is an exploded perspective view of an illustrative three axesimage stabilization system (500). The three axes image stabilizationsystem (500) includes an X-Y stage (530) and a rotational stage (525)which is nested into the interior of the X-Y stage (530). The focalplane (510) is contained within a carrier (515). The carrier (515) whichis attached to the upper surface of the rotational stage (525). Anelectrical connector (520) allows the electrical signals produced by theindividual pixels which make up the focal plane to be read. These stages(525, 530) move the focal plane to compensate for higher frequencyjitter.

According to one illustrative example, the rotation stage (525) and X-Ystage (530) may be actuated by piezo electric actuators. Piezo electricactuators apply a voltage to a piezo active material which expands orcontracts a distance which corresponds to the applied voltage. Typicallythis expansion or contraction is less than 1% of the overall size of thepiezo active element. This change in the geometry of the piezo activematerial is extremely rapid and can produce a large amount of force.

In one embodiment, the piezo stages may be formed from a single monolithpiece of metal which has been machined to form flexural joints which aremoved by the piezo-electric actuators. This approach results in anextremely rigid stage which prevents the undesirable motion of the focalplane and allows for high frequency control of the focal plane position.For example, in the configuration illustrated in FIG. 5, the piezostages (525, 530) may exhibit natural frequencies between approximately300 to 500 Hz. Less rigid optical stages can be undesirable because theymay allow the focal plane to move out of focus. Further, rigid stagesare desirable because the data generated by angular rate sensors locatedin a separate location can be used to directly determine the motion ofthe focal plane to an acceptable level of accuracy.

According to one illustrative embodiment, the X-Y stage (530) canproduce motions on the order of 100 microns and the rotational stage canproduce motion on the order of 10 milliradians. Although this range ofmotion is relatively small, the stages produce enough travel toeffectively cancel undesirable jitter-induced smearing. Integrationtimes for many optical systems are typically on the order ofmilliseconds. Consequently, the magnitude of jitter-induced imagetranslation on the focal plane during the integration period can berelatively small, typically on the order of 1 to 100 microns. Themagnitude of the image translation can be a function of a number ofparameters including the optical configuration of the system.

Each axis of the stages (525, 530) may also include a sensor whichprovides information about the current position of the stage. Forexample, various capacitive, inductive, optical or strain gage basedsensors may be incorporated into the piezo stage to provide the desiredfeedback regarding the stage's current position.

FIG. 6 is an exploded perspective view of the three axis imagestabilization system incorporated into the ball (410) of a two axisgimbaled imaging system (400, FIG. 4). According to one illustrativeembodiment, an optical bench (635) provides a rigid and stable platformto which the other components are mounted. The X-Y stage (530) ismounted to the under side of the optical bench, with the rotationalstage (525) mounted within the central cavity of the X-Y stage (530).The focal plane (510) is mounted to the upper surface of the rotationalstage (525). According to one illustrative embodiment, the focal plane(510) may be an infrared (IR) detector which senses optical wavelengthsin the infrared portion of the electromagnetic spectrum. Infrared focalplanes can provide a number of benefits including night vision, highvisibility of heat sources, detection of chemicals, and otheradvantages. However, infrared focal planes typically have longerintegration times and are consequently more susceptible tojitter-induced smearing.

IR optics (630) are attached to the optical bench over the focal plane(510) such that optical energy from the exterior scene is focused ontothe focal plane (510). According to one illustrative embodiment, anindependent visible camera (615) with its associated visible optics(620) may also be included in the ball (410).

Three angular rate sensors (625) are attached to the optical bench (635)in three different orientations. According to one illustrativeembodiment, these angular rate sensors (625) detect rotations aboutthree orthogonal axes. According to one illustrative embodiment, theangular rate sensors may be mechanical gyroscopes, ring lasergyroscopes, magnetohydrodynamic rate sensors,micro-electro-mechanical-systems (MEMS) gyroscopes or the like. Theangular rate sensors (625) may be selected according to variousparameters, such as values for bandwidth, accuracy, drift, and the like.The signals generated by the angular rate sensors (625) are utilized bythe image stabilization control system to determine how to move thefocal plane.

Additionally or alternatively, other methods of measuring jitter may beused. In some embodiments, a sensor array may be utilized to detecteither the absolute angle or the angular rate or both. Thesemeasurements may be made from a variety of locations, including at theoptics (620, 630), at the gimbal (405), or at a focal plane (510)itself. For example, the imagery generated by the visible camera (615)may be utilized to sense angular rotations of the optical assembly. Thevisible camera (615) may have a much higher frame rate than the IRcamera. By using a real time change detection algorithm or othersuitable method, changes between frames in the visible data could beused to detect jitter. This illustrative method of sensing jitter couldbe used to supplement the angular rate sensors (625) or could be usedindependently.

A front cover (610) and a rear cover (640) attach to the optical bench(635) to protect the optical components and form the outer shell of theball (410). The front cover (610) has two apertures (415) through whichthe IR and visible sensors (515, 615) receive optical energy from thesurrounding scene. These apertures (415) may be covered by windows toprotect the interior components. According to one illustrativeembodiment, the front cover (610) and rear cover (640) may formhermetical seals with the optical bench (635) to provide a controlledenvironment within the ball (410).

FIG. 7 is a cross-sectional diagram of the illustrative imagestabilization system incorporated into the gimbaled imaging system(400). The resulting system (400) has five controlled degrees offreedom: two coarse rotational degrees of freedom provided by the twoaxis gimbal (405) and finer three degrees of freedom provided by theimage stabilization system (500, FIG. 5). As discussed above, theazimuth stage (700) and the elevation drive (710) of the gimbal (405)provide pointing and lower frequency corrections. The elevation drive(710) is connected to a pivot point in the gimbal arms and rotates theball (410) about its center.

For higher frequency image stabilization, the three axis imagestabilization system (500, FIG. 5) actuates the X-Y stage (530) and therotation stage (525) to cancel out undesirable motion of the imageacross the focal plane (510). The piezoelectric actuators may beactivated to move the focal plane array (410) about the X, Y, and Z axesat a rate, displacement, or both, equal and opposite to those imposed byvibration or jitter. As discussed above, the optical bench (625)provides a common reference point and stable platform for the variouscomponents which make up the ball (410). The X-Y stage (530) controlsmotion parallel to the plane of the focal plane (510) and the rotationstage (525) provides rotation about a bore axis (720) which passesthrough the center of the IR optics (630).

When the control system determines that a rotation of the optical systemhas occurred during an integration period, the appropriate controlsignals are sent to the X-Y stage (530) and the rotation stage (525).Actuation of the X-Y stage (530) translates both the attached rotationalstage (525) and the focal plane (510). Rotations of the rotational stage(525) move only the attached focal plane (510).

FIG. 8 is a flow chart showing an illustrative control system (800) fora three axes piezo stabilized imaging system. According to oneillustrative embodiment, angular rate sensor signals (815) enter thesystem from the angular sensors (625, FIG. 6). These signals (815) arereceived by a filtering module (820) which pre-filters the sensorsignals (815). According to one illustrative embodiment, the filteringmodule (820) may include a high pass filter which shapes the response inthe operating frequency band of the image stabilization system. Thefiltered signals are then passed to a signal conversion module (825).The signal conversion module (825) converts the filtered signals into anangular rate by applying sensor specific calibrations. For example, eachsensor may have an angular sensitivity which can be expressed in termsof radians per second per volt. The signal conversion module (825)converts the signal voltage by applying the angular sensitivity toproduce angular rate data expressed in terms of radians per second. Thisoutput data is received by an integrator (835) which integrates theangular rate data with respect to time to generate an instantaneousrotation in radians. This rotation is mapped into optical space by themapping module (845). According to one illustrative embodiment, themapping module (845) converts the rotation in radians into displacementof the image across the focal plane. For example, the mapping module(845) may use geometric and optical properties of the system to convertthe rotation of the optical bench into displacement of the image acrossthe focal plane.

This displacement (850) is passed into a summing module (860) where itis combined with the measured piezo position (880) and the output of apiezo transfer function (855). The measured piezo position (880)represents the current position of the piezo stage, and consequently,the current position of the focal plane. The piezo feed-forward transferfunction (855) is a model of the piezo stage behavior which providesinformation about the frequency domain response of the piezo stage.

If the combination of the three inputs to the summing module (860)results a zero, the focal plane is already in the desired position andno response is necessary. If the result of the summing function isnon-zero, the focal plane needs to be moved to a new location tocompensate for jitter-induced motion of the image across the focalplane. This is output as an error (863). This error (863) is received bya controller (865) which controls the motion of the piezo stages.According to one illustrative embodiment, the controller (865) may be aproportional-integral-derivative (PID) controller. The PID controlleruses a control loop to correct for the error (863) by outputting controlsignals to the piezo stages and using capacitive or inductive sensorswithin the piezo stages to determine if the desired motion was produced.

According to one illustrative embodiment, the output of the controller(865) may be filtered by an output filter module (870). The outputfilter module (870) may include a number of functions, such as notchfilters which prevent the excitation of undesirable structural modes anda low pass filter which imposes a cut-off frequency on the controller.The notch filters allow the controller to continue to control the piezostages at frequencies higher than one or more structural modes. The lowpass filter limits the control signals to a desired frequency range andreduces undesirable high frequency noise. A piezo command (875) isgenerated by the output filter module (870) and passed to the piezostage. The control system (800) described above can be replicated foreach control axis within the image stabilization system and can correctfor jitter frequencies below one hertz up to hundreds of hertz.

FIG. 9 is a flow chart of an illustrative method for stabilizing animage system using a three-axes piezoelectric-stabilized, opticalsystem. In a first step, an angular rate of rotation of the opticalassembly is measured (step 900). As described above, this measurementmay be made using a number of methods, including magnetohydrodynamicgyroscopes. The current position of each of the three controllable axesof the piezo stages are then measured (step 910). According to oneillustrative embodiment, the X and Y axes measurements are produced byinductive sensors and the rotational measurement is produced by a straingage. The angular rates are then integrated to determine the absoluteshort term attitude of the optical assembly (step 920). The absoluteattitude is then mapped into motion of the image on the focal plane(step 930). The current position of the three controllable axes is thencompared to the desired position of the focal plane (step 940). If thecurrent position of the three controllable axes is substantially equalto the desired position, no action is taken. However, when an error isdetected, the appropriate piezo stages are actuated to minimize theerror, thereby reducing jitter-induced smear (step 950). This process isrepeated throughout the integration period. After the integration periodends, the current frame is read out of the focal plane array and thepiezo stages are reset to their neutral positions to prepare for thenext integration period (step 960).

The preceding description has been presented only to illustrate anddescribe embodiments and examples of the principles described. Thisdescription is not intended to be exhaustive or to limit theseprinciples to any precise form disclosed. Many modifications andvariations are possible in light of the above teaching.

1. A system comprising: an optical assembly configured to receiveelectromagnetic radiation emitted by a target and produce an image ofthe target; a focal plane array configured to receive the image andintegrate at least a portion of the electromagnetic radiation making upthe image to produce an electrical representation of the image; sensorsconfigured to provide kinematic data; a control system receiving thekinematic data and estimating jitter-induced motion of the image on thefocal plane and outputting a control signal; and piezo-electricactuators configured to receive the control signal, and to translate thefocal plane along two orthogonal axes, and to rotate the focal planeabout a third orthogonal axis, such that jitter-induced motion of theimage on the focal plane is reduced, wherein the piezo-electricactuators comprise an X-Y stage that has been machined to form flexuraljoints that are moved by piezo-electric material.
 2. The system of claim1, wherein the third orthogonal axis is substantially parallel to a boreaxis of the optical assembly.
 3. The system of claim 1, wherein thethird orthogonal axis is substantially collinear with a bore axis of theoptical assembly.
 4. The system of claim 1, wherein the system isconfigured to reduce jitter-induced motion of the image on the focalplane in a range which includes frequencies of 25 Hz to 500 Hz.
 5. Thesystem of claim 1, wherein the piezo-electric actuators further comprisea rotation stage, the X-Y stage producing translations on the order of100 microns and the rotation stage producing rotations on the order of10 milliradians.
 6. The system of claim 5, wherein the focal plane isdirectly attached to the rotation stage, the rotation stage beingattached to the X-Y stage such that actuation of the X-Y stage movesboth the rotation stage and the focal plane.
 7. The system of claim 6,in which natural modes of the X-Y stage, when supporting the rotationstage and the focal plane, are greater than 300 Hz.
 8. The system ofclaim 6, in which natural modes of the rotation stage, when supportingthe focal plane, are greater than 300 Hz.
 9. The system of claim 1,further comprising a multi-axis gimbal, the multi-axis gimbal providingpointing capabilities to the system.
 10. The system of claim 1, whereinthe sensors measure angular displacement.
 11. The system of claim 1,wherein the sensors are angular rate sensors configured to provideangular rates of motion about three orthogonal axes.
 12. The system ofclaim 1, wherein the control system comprises notch filters, the notchfilters reducing excitation of resonant frequencies within the system;the control system further comprising a feed-forward transfer functionwhich provides frequency domain response information of the actuator.13. The system of claim 1, wherein the control system is configured toreceive data from the sensors and calculate a measured piezo position;the control system summing the measured piezo position with thejitter-induced motion of the image on the focal plane to find apositional error of the focal plane.
 14. The system of claim 1, whereinthe piezo-electric actuators comprise a flexure and at least one straingage position sensor attached to the flexure.
 15. A system for reducingjitter-induced smear on an infrared focal plane comprising: an infraredfocal plane array configured to receive electromagnetic radiation andintegrate at least a portion of the electromagnetic radiation to producean electrical representation of an image; a gimbaled optical assemblyconfigured to receive electromagnetic radiation emitted by a target andfocus the image of the target on the infrared focal plane array;gyroscopic sensors configured to provide angular rate data in threeorthogonal axes; a control system receiving the angular rate data andestimating jitter-induced motion of the image on the focal plane andoutputting a control signal, the control system comprising notchfilters, the notch filters reducing excitation of structural resonantfrequencies within the system; piezo-electric actuators configured toreceive the control signal and to translate the infrared focal planealong two orthogonal axes and rotate the infrared focal plane about abore axis such that jitter-induced motion of the image on the infraredfocal plane is reduced; and a visible camera having a higher frame ratethan the infrared focal plane array, in which changes between imageframes produced by the visible camera are analyzed to sense angularrotations of the system to supplement angular rate data produced by thegyroscopic sensors.
 16. The system of claim 15, wherein the systemcontrols two coarse rotational degrees of freedom provided by a two axisgimbal and three finer degrees of freedom actuated by the piezo-electricactuators.
 17. A method for reducing jitter-induced smear in an imagingsystem comprising: sensing jitter of the imaging system; calculatingjitter-induced motion of electromagnetic energy on a focal plane; androtating said focal plane about a bore sight axis of the imaging systemusing a piezo-electric stabilization system to reduce the jitter-inducedsmear within the imaging system, wherein the piezo-electricstabilization system comprises piezo-electric actuators comprising anX-Y stage which has been machined to form flexural joints which aremoved by piezo-electric material.
 18. The method of claim 17, wherein:the sensing comprises measuring angular rates of rotation of the imagingsystem in three orthogonal axes; and the calculating comprises:integrating the angular rates of rotation to determine a short termattitude of the imaging system; mapping the short term attitude of theimaging system to determine the jitter-induced motion; and calculating ademanded position of the focal plane to reduce the jitter-induced motionof the electromagnetic energy on said focal plane.